Funds are requested to purchase a state-of-the-art electron spin resonance (ESR) spectrometer with mass storage capability and accessories such as variable temperature facility and loop gap resonator. The requested instrument is a Bruker ESP/300 ESR which will make modern ESR spectroscopy readily accessible to various researcher to pursue PHS funded research projects. Programs supported with this instrument would encompass: (A) spin assays with microgram quantities of nucleic acid binding proteins and spin labeled oligonucleotides and spin labeled nucleic acids as probes to gain a more detailed understanding of the parameters playing a central role in genetic expression and regulation; (B) elucidation of the mechanism of the chemical reactions required to prepare lignan anti-tumor prototypes such as steganacin and podophyllotoxin whose synthesis are based on oxidative coupling reactions; (C) detection of oxygen derived free radicals by spin trapping in tissues reperfused after anoxia or ishemia of isolated segments as well as of intact segments of intestines of mongrel dogs and domestic farm pigs; (D) investigation of nitrosyl complexes of TcII and other paramagnetic technetium complexes at both the macroscopic level for classical spectroscopic characterization and at the 10-8 M concentration level to gain information about the chemistry and biochemistry of "no carrier added" 99mTc radiopharmaceuticals.